1. Field of the Invention
The invention relates to a cell scraper for scraping samples of tissue that accumulate in a tissue culture vessel.
2. Description of the Related Art
Many laboratory procedures require the cultivation of tissues for subsequent analysis and diagnostic tests. The tissues are cultivated in tissue culture vessels, such as flasks or petri dishes. A typical tissue culture flask is a low profile rectangular vessel with a top wall, a bottom wall and a plurality of interconnected side walls. One side wall may include an opening and a tubular neck may project angularly up from the opening to provide access to the interior of the tissue culture vessel. A cap may be mounted removably on the tubular neck for sealing the tissue culture vessel. Other tissue culture dishes include a bottom wall, a side wall enclosure and an open top. A cover may then be mounted removably to the open top of the side walls for selectively enclosing the interior of the tissue culture vessel.
Tissue culture vessels are employed by depositing a controlled amount of a liquid growth medium in the vessel. A small sample of the tissue that is to be cultivated then is deposited into the vessel. The vessel is closed by placing the cap over the tubular neck or by placing the top wall across the open top defined by the side walls. The vessel then is stored in an environment that is conducive to tissue growth. Tissue growing in the vessel must be removed and analyzed periodically. The growing tissue is likely to attach itself to the bottom wall of the vessel, and hence must be scraped from the bottom wall for analysis.
Cell scrapers are employed for removing tissue from the bottom surface of a tissue culture vessel. The typical cell scraper includes a long thin handle unitarily molded from a rigid plastic material. The handle typically tapers from a relatively large proximal end to a relatively small distal end. For example, the proximal end of the handle is likely to be approximately 0.25 inch in diameter, while the distal end is likely to be about 0.125 inch in diameter. The proximal end of the handle may be knurled to facilitate gripping by a laboratory technician. The distal end of the handle is molded to include two hinge pins.
The known cell scraper also includes a scraper blade molded unitarily from plastic, and may the same plastic as the handle. The blade includes a planar scraping edge and a pair of opposed mounting apertures that can be snapped into engagement with the hinge pins of the handle. The dimensions of the blade will vary depending upon the intended application, and specifically in accordance with the size of the tissue culture vessel. For example, a small blade is likely to be only slightly in excess of 0.5 inch wide, while a large blade is likely to be slightly in excess of one inch.
The hinge pins for mounting the blade to the handle typically are very small. For example, a hinge pin typically has a diameter in the range of 0.06-0.1 inch, and a length of comparable dimensions. As a result, the mechanical connection between the blade and the handle of the typical cell scraper is weak. The very small dimensions create the potential for improper mounting of the blade on the handle. Hence, the mounting of the blade to the handle is time consuming and costly and must be subject to considerable quality control checking.
The cell scraper typically is shipped to the laboratory in a sterile package formed by opposed layers secured in face-to-face relationship around the cell scraper. The package is opened immediately prior to use by peeling the layers away from one another and removing the cell scraper from the opened package. The laboratory technician opens the tissue culture vessel. The technician then holds the knurled proximal end of the handle in one hand while inserting the blade at the distal end of the scraper into the tissue culture vessel. The blade pivots about the hinge pins to align with the bottom surface of the vessel in response to forces exerted on the handle by the technician. The technician then slides the blade across the bottom surface of the tissue culture vessel, while maintain a perpendicular force to the growth surface, so that a sample of the cultured cells can be scraped from the bottom. The cells are then washed from the tissue culture vessel for analysis. Perpendicular and lateral forces exerted on the blade easily can dislodge the blade from the handle of the cell scraper. These forces can be exerted during the initial insertion of the blade into the tissue culture vessel, during the removal of the blade from the tissue culture vessel or during the cell scraping process. The separated blade cannot be retrieved easily without adversely affecting the tissue culturing process. Hence, the laboratory must then incur the expense for an additional cell scraper and creates the risk of contaminating the tissue culture vessel.
Occasionally it may be necessary to access difficult to reach areas of a tissue culture vessel, such as corners of the vessel or areas near the opening to a flask of the vessel. The pivoting of the blade on the handle may facilitate access to remote areas of the tissue culture vessel. However, the rigid plastic blade is not ideal for removing cell cultures from surfaces that are difficult to reach. A more resilient blade could be more effective for removing cell cultures from surfaces that are not perfectly planar. However, a more resilient blade would not be as effective for gripping the hinge pins of the scraper handle and would separate from the hinge pins more easily.
The knurling that is molded into the handle of the cell scraper contributes somewhat to the digital manipulation of the scraper. However, knurling can have only a minimal effect on the ability to manipulate the scraper in view of the relatively small cross-section of the handle.
Some tools have been molded with handles formed from two different types of materials to facilitate gripping. A first material is a more rigid thermoplastic and provides structural support for the handle. A second material is over-molded or co-molded with the more rigid material and is more resilient. The more resilient material facilitates gripping. Such over-molding is commonly used in handles of toothbrushes and other hand-held tools. The more rigid thermoplastic material then extends from the gripping region of the toothbrush or other tool to the distal working end of the toothbrush or tool.